1. Field of the Invention
The present invention is directed to a hearing aid system, and in particular to such a system having a wireless remote control of at least some of the components of the hearing aid worn in the ear of a user.
2. Description of the Prior Art
A hearing aid having an in-the-ear unit and a control unit remote therefrom, with the control unit wirelessly transmitting control signals to the in-the-ear unit, is described in German OS 19 38 381. As is known, hearing aids should be as small as possible in order to permit the hearing aid to worn inconspicuously. Miniature hearing aids worn in the auditory canal are known. In this type of hearing aid, at least the volume, but also a number of other functions critical to adapting the hearing aid to different hearing situations, should be variable as much as possible. It is necessary that adjustment devices be provided which are accessible by the user while the hearing aid is functioning in contact with the user. Moreover, the range of manipulation during adjustment should be discernable.
The hearing aid described in German OS 19 38 381 has components divided into two housings, one housing containing a transmitter and the other housing containing the hearing aid which is worn in the ear. Signals are wirelessly transmitted from the transmitter to the in-the-ear unit, which includes a receiver tuned to the transmitter. The housing for the in-the-ear hearing aid, however, provides very little extra space for the receiver. Typical in-the-ear hearing aids worn in the auditory canal generally have less than 100 cubic mm available for the incorporation of a remote control receiver. In German OS 19 38 381, therefore, a receiver was provided which operates without the need for an additional sensor, an antenna or the like.
Another hearing aid is described in German OS 34 31 584, having a remote control unit wherein the microphone of the hearing aid is used both as a receiver for the control signals and as a conventional microphone. Inaudible sound, such as ultrasound, is used for the transmission of the control signals. The ultrasound transmitter is disposed in a control device, and control signals are generated via a keyboard and are generated as an output by a speaker. In the in-the-ear portion of the this hearing aid system, the signals received by the microphone are deployed to two branches, one branch leading to the sound generating portion of the hearing aid, and the other branch leading to a control portion of the hearing aid via a filter which blocks all signals except the ultrasound signals.
The hearing aid described in German OS 34 31 584 is substantially free of switches and other control-associated components by virtue of the use of remote control. The following functions occur in sequence in the remote operation. After the actuation of an operating key, the transmitter electronics identifies this event, and encodes a control signal in accordance with the desired function, and this encoded control signal is then transmitted. The inverse operational sequence occurs in the receiver. The signal is received, decoded, and identified, and the corresponding electronic adjustment element is actuated. Other types of signal transmission, such as electromagnetic transmission and infrared transmission are described in German OS 24 07 726 for the remote transmission of hearing aid control signals, as well as the aforementioned ultrasound transmission.
Each of the above-described types of signal transmission have a transmission path associated therewith which can be undesirably influenced by specific sources of disturbance. For electromagnetic transmission, for example, a large number of electromagnetic sources of disturbance may contribute to degrading the transmission path, and thus must be taken into consideration. Moreover, the availability of transmission frequencies is very limited due to regulations in various nations, and differs greatly from country to country. Infrared transmission can be disturbed by direct solar irradiation on the receiver diode, which must of necessity be located at a exposed location at the hearing aid.
The ultrasound transmission path can be disturbed by radio frequency sound sources such as, for example, an ultrasound cleaning bath.
Moreover, additional component parts are required for reception of the control signals using electromagnetic transmission or infrared transmission, whereas the microphone, which is already present in the hearing aid, can be used for ultrasound transmission. It has been shown, however, that as a result of known, special propagation conditions of ultrasound, the main emission direction of the speaker in the remote control transmitter must be directed rather precisely in the direction of the opening of the auditory canal, in order to be able to drive the in-the-ear hearing aid. To this end, the transmitter must be lifted relatively high, or must be held relatively far from the body. Aiming is relatively difficult for persons having little capability to perceive things in three dimensions, because this aiming must be undertaken without direct visual control. Moreover, many patients find such a manipulation undesirable, because it may direct the attention of persons with whom they are speaking to their hearing impediment. These problems can be magnified if the hearing aid is seated more deeply in the auditory canal. This is a particular problem with smaller auditory canal hearing aids, but can also arise in implanted hearing aids as described in German OS 36 17 118.